Hot fluid injection into hydrocarbon resevoirs

ABSTRACT

Hot fluid may be injected into a subterranean hydrocarbon reservoir with little heat loss through the casing walls on the way down to the injection zone by placing tubing inside the casing of an injection well and injecting a hot fluid or vapor into the tubing and a cold fluid into the annulus between the tubing and casing.

United States Patent 1191 Allen et al.

[ Nov. 27, 1973 HOT FLUID INJECTION INTO 1,237,139 8/1917 Yeomans166/272 x "YDRQCARBON RESERVOIRS 3,456,730 7/1969 Lange 166/272 X3,498,381 3 1970 13611611 1161, Jr. 166 303 [75] Inventors: Joseph C.Allen; Bellalre, Yick- 3,221,813 12/1965 CIOSIIBIIII et al.....166/272'x Mow Shum, Houston, both of Tex. 3,386,512 6/1968 Bloom 166/3033,380,530 4/1968 McConnell et al. 166 303 [73] Assignee: Texaco Inc.,New York, NY

*Wnw Primary Examiner-Stephen .l. Novosad [22] 1972 Attomey-Thomas l-l.Whaley et al.

[21] Appl. No.: 229,927

[57] ABSTRACT [52 us. 01. 166 303 Hot fluid y be injected into aSubterranean y 51 Int. Cl E21b 43/24 carbon reservoir with little heatloss through the [58] Field 61 Search 166/303, 272, 302, s Walls on they down to the injection zone y 166/305 R placing tubing inside thecasing of an injection well and injecting a hot fluid or vapor into thetubing and a [56] a Cited cold fluid into the annulus between the tubingand UNITED STATES PATENTS 3,559,738 2 1971 Spillette 166 303 7 Claims, 3Drawing Figures 3,186,484 6 1965 Waterman 166 272 x HOT FLU/D- "i 10c010 FLU/D 3 I i EXTRANEOUS 1; FORMAT/0N5 3 1 8 1 i 4 i 4 f I Y L\\\(YA/K t/2,, i #EYHYDRO- L; CARBON BEARING I V v e RESERVOIR A x/Q \r'QQQ; [6,, l I

PATENTEB NOV 27 I975 COLD FLU/D EXTRANEOUS 4 FORMA T/ONS R S RV HYDEO vCARBON BEARING FIG 2 COMPARATIVE HEAT LOSSES k S L 0 lbboo HOT FLUIDINJECTION INTO HYDROCARBON RESERVOIRS BACKGROUND OF THE INVENTION 1.Field of the Invention This invention is concerned with the field ofsecondary recovery of hydrocarbons from subterranean reservoirs by theinjection of hot fluid into the reservoir.

2. Discussion of the Prior Art In many hydrocarbon producing areas thereare reservoirs where production is no longer commercially feasible dueto the fact that the original pressure in the hydrocarbon stratum hasbeen exhausted to the extent that hydrocarbons will no longer movethrough the formation into production wells in sufficient quantities topermit profitable operation. Usually, however, these reservoirs in facthave more oil remaining in them than has been produced.

Also, many reservoirs contain very'viscous hydrocarbons. This highviscosity impedes flow and much of these viscous hydrocarbons aretrapped in the reservoirs even while relatively high reservoirpressuresremain. Attempts to recover thesehydrocarbons have included theinjection of a fluid into the reservoir to increase the pressure in thereservoir and displace the hydrocarbons to production wells where theyare produced. These fluids are typically aqueous, gaseous, somehydrocarbon or a mixture of materials. It has been recognized that thetemperature of the injected fluids have a great influence on theefficiency of the recovery process. The hydrocarbons in the reservoirwill flow more readily if they are heated by'the injected fluid with aconsequent reduction in their viscosity.

Therefore, it is often necessary and more efficient to inject a hotfluid into the-reservoir.

However, in the past, cost of heating the great volumes of injectionfluids has'been inflated because of the great losses of heat from 'thehot injection fluid through the sides of the wellintoextraneous'formations on the way down the injection well bore tothehy'clrocarbon formation of interest. Thus, it has previously beennecessary to heat the injection fluids at the surface to much highertemperaturesthan is desired at the injection point. Attempts have beenmade to decrease the amount of injection fluid heat loss as it travelsdown the injection well to the point of injection. For instance, tubingmay be installed in the injection well with devices to centralize itin'the well bore andprevent its contact with the casing where rapid heatconduction would increase the flow of heat from the injection fluid.

However, much heat is still lost through the tubing walls into theannularspaces between the tubing and casing and then to extraneousformations in the earth. Other methods such as insulation have also beenattempted but leave much to be desired because of the expense involved.

Also, due to depths of some hydrocarbon formations pressure limitationsare placed on surface injection facilities which prevent'hot enoughfluid from-being injected at the surface.

SUMMARY OF THE INVENTION Our invention is a method of injecting a'hotfluid into a subterranean hydrocarbon reservoir with a minimum of heatloss from the injected fluid to' the extraneous formations whichcomprisesproviding tubular means inside of well casing and injectingcoldfluid into the annular space between the tubular means and thecasing wall while injecting a hot fluid into the tubular means. Bothfluids being injected at such a rate that the cold fluid is heated bythe hot fluid in the tubular means and reaches the desired temperatureof injection at approximately the same time it reaches the depth of thehydrocarbon reservoir into which injection is to take place.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 depicts an arrangement wherebyan open ended string of tubing penetrates a well wherein hot fluid maybe injected into the tubing and cold fluid into the annular spacebetween the tubing and the casing.

FIG. 2 compares the heat lost to the formations above the hydrocarbonzone of interest using prior art hot water injection techniques and themethod of our invention as illustrated by FIG. 1.

FIG. 3 depicts an arrangement wherein a closed tubing arrangement isprovided in the well so that the hot fluid may be circulated into thewell and out without contacting the cold fluid injected into the annularspace between the tubing and the casing.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Our invention may be moreclearly understood by referring to the attached figures which illustratetypical embodiments of our invention. FIG. 1 shows an injectionwellpenetrating the earth with perforations in communication with ahydrocarbon bearing reservoir.

A single string of tubing '10 penetrates the well to a depth above theperforations 11. The tubing is open at the bottomandis therefore incommunication with the other materialsin the well. Steam, for example,is injected into the tubing and cold water, for example, is

injected into the annular space between the tubing and casing. The ratesof injection are adjusted so that water in the annular space heats upslowly and reaches the desired temperature .for injection just as thewater reaches the depth of the perforations. In this manner a minimum ofheat will be lost to extraneous formations above the hydrocarbon bearingreservoir of interest. The heat of the steam is used to heatthe water,and so long as the water remains cooler than the subterranean ambienttemperatures no heat will be lost. In fact, heat will be added to' thewater from the surrounding formations in the earth. Only when thetemperature of the water exceeds the temperature of the surroundingformations will any heat be wasted. By heat conduction calculationsknown to those skilled in the art it will be possible to calculate therate of steam and water injection to allow the water to travel themaximum distance into the earth before its temperature exceeds thetemperature of the surrounding formations in'the earth. In this way aminimum amount of heat will be lost to extraneous earth formations. Itis clear that this method providesa great savings in heat energy andthus a corresponding economic advantage as shown by the followingillustration.

The total heat delivered to the hydrocarbon formation by water-steaminjection was. calculated for two theoretical situations as noted below.

CASE I (PRIOR ART) Saturated steam, at 1000 psia, 545F., 80 percentquality and 270 barrels per day (BPD), was mixed with water, at 1000psia, F and 260 BPD, adiabatically.

The resulting mixture, approximately 3 percent quality steam at 545F.,1000 psia, was injected into 2 "/s in. tubing suspended at 4000 feet ina well with 7 inch casing.

CASE II (IVIETHOD OF THE INVENTION) Using the same tubing and casingdiameters, the heat delivered to the formation was calculated using thesame steam and water properties given in Case I. However, in this caseonly steam was injected into the tubing and the water was injected intothe tubing-casing annulus.

Results for each case are represented in FIG. 2 by plotting the heatlost to the overburden formation as a function of time. The heat lossfrom the well bore to the overburden formation was determined bystandard mathematical techniques using a computer program. Theory anddevelopment of the calculation procedure is based on aquasi-steady-state method. Case II results were developed by standardmathematical techniques using a computer program. The energy istransferred from the hot fluid to the cold water in the annulus, and,subsequently to the overburden formations above the formation whichaccepts the injected fluid. FIG. 2 shows that the heat loss to theextraneous formations would be cut approximately in half using themethod of our invention. Due to the transient nature of the problem, theprinciple of superposition was used to determine the thermal energytransferred from the water in the annulus to the overburden formations.Solutions were obtained using established energy balance equations withnumerical iteration. Briefly the solution procedure was as follows:

1. Assume a T the outlet temperature of the injected steam at a rate ofS (lb/hr).

Due to the large values of the convective heat transfer coefflcient andwell depth, I-I (ft), the outlet temperature of the injected water, Twould be equal to T 2. Thermal energy transfer calculation:

Thermal energy given up by the steam is Q, (T,, T,.,) S SH X (BTU/hr) 1where H is the latent heat of the injected steam. (BTU/lb),

and X is the inlet steam quality.

Thermal energy gained by the injected water in the annulus is Qu: wo m)W where W is the water injection rate (lb/hr).

3. Thermal energy transfer from the water in annulus to the surroundingformation by conduction, is calculated as follows:

IOg A a0 a log oB azlog o B (1310810 8 a. log B 3 where A R F/KT,dimensionless heat flux.

B aJ/R dimensionless time,

a,,, 11,, a a a and a are constants,

R is the casing radius, ft.

K and a are the thermal conductivity (BTU/hr-ftF.) and diffusivity (ft/hr), respectively.

I is time, hr.

T is the temperature difference between the casing surface and theformation, F.

F is the heat flux, BTU/hr-ft. Then Q (4 where A is the casing surfacearea, ft. Due to the transient nature of this problem, the method ofsuperposition must be employed as illustrated as follows:

a. At the end of the 1st time step, say t,,

wo ami. wm,l wi wo, 1) T is the average water temperature. 1 n fo) whereT, is the ground surface temperature and T is the sand face formationtemperature, F. F is calculated from equation (3) with T= T 1 T, and t=t, b. At the end of the 2nd time step, i.e., t= t t, t

wo wo. 2 wm. 2 wi wo. 2) The method of superposition says where F, iscalculated with T= T 1 T,, and t F is calculated with T= T 2 T and t z,t and so on 4. An energy balance required If equation (5) can not besatisfied within a preset tolerance, a new value of T is selected andcalculations from steps 1 to 4 are repeated. Otherwise, solution isadvanced one time step by starting the calculation from step 1.

Some conditions may exist, however, which would prevent the convenientoperation of the procedure illustrated by FIG. 1 above. FIG. 3illustrates a procedure which is another typical embodiment of ourinvention. FIG. 3 is a closed tubing arrangement wherein all thebenefits embodied in the open tubing arrangement of FIG. 1 are providedwith the added feature of segregation between the hot fluid in thetubing and the cold fluid to be heated in the annular space between thetubing and casing. A large string of closed end tubing 10 penetrates awell 11 and a smaller string of open end tubing 12 penetrates the closedend string of tubing. A hot fluid, steam, for instance, is circulateddown through the annular space 13 between the tubing strings and upthrough the small inside tubing string. A cold fluid, water, forinstance, is injected down the annular space 14 between the large tubingstrings and the well casing. This water is heated on the way down thewell bore in the manner described in FIG. 1 by contacting the heatedtubing string 10 and is injected into a hydrocarbon reservoir. Onceagain injection rates may be adjusted so that the water heats as slowlyas possible and attains its desired temperature at the depth of thehydrocarbon formation in which it is to be injected. The method of FIG.3 may be used in shallow formations where the temperature of theinjected steam is limited to the injection pressure which is in turnlimited by the shallow depth. Since injecting steam at an excesspressure to provide high temperature might lift the overburden thusrupturing the earth formations with harmful consequences known to thosein the art of oil production, the open tubing arrangement of FIG. 1cannot be desirable since the pressure of the steam is communicated tothe earth formations. Also, where it is desired to inject superheatedsteam into a shallow formation the method of FIG. 3 would providesuperheated steam at the hydrocarbon reservoir depth while injectingonly saturated steam at the surface. For examnle mt dst 1 a 3 Pounds Pe339%.? n is injected into the annulus 14. Saturated steam at 600 poundsper square inch is injected into the annulus 13 and circulates outthrough the small string of tubing 12. The 300 psi steam is superheatedby the 600 psi steam without the high 600 psi pressure affecting thehydrocarbon reservoir. Thus, in the shallow formations high pressurewhich may rupture the formations will not have to be used in order toattain high fluid injection temperatures since the high pressure fluidin the closed circulating tubing arrangement is isolated from theformation. Another example with the open tubing embodiment of FIG. 1would be inapplicable is where the hydrocarbon reservoir is very deep.Here the steam would be condensed to water for a considerable depth inthe well. Thus, very high steam pressure would be necessary in order tomaintain the desired rate of steam injection.

Also, the method of our invention allows a hotter fluid to enter theshallow formation than would be possible by injecting hot fluid from thesurface. For example, consider a reservoir 600 feet below the surface.By a typical standard practice the overburden at 600 feet ssa a e t e 99P nd EQS HQUQLQL pound per square inch per foot of depth. Above thispressure the formation is likely to fracture or rupture. At 600 feet thehydrostatic heat is 260 pounds per square inch. Thus, the maximumsurface injection pressure is 600 minus 260 340 pounds per square inch.At this surface pressure the maximum temperature of water is 430F. andthe heat content of the water is 408 BTU per pound. Heat losses on theway down would cause the water to enter the formation at an even lowertemperature. However, using the method of our invention as depicted inFIG. 3 steam may be injected into the tubing strings as shown and waterinto the annulus between the large tubing and the casing. The water isinjected into the formation at 486F. at 600 pounds per square inch sinceit picked up its heat on the way down and was not limited in temperatureby the surface injection temperature and pressure. At 486F. the waterenters the formation with a heat content of 471 BTU per pound. Twodistinct advantages are apparent, the heat flow rate is increased by15.4 percent and the material flow rate into the formation is increasedby 14.5 percent over the surface heating of the water.

Heat flow rate increase:

4sa 4ao 471 408 Also, the basic advantage of our invention, theconservation of heat energy is also gained. The above example assumesfor illustration purposes no heat loss of the water injected at 430F. atthe surface when in fact there would be heat loss on the way to theformation. When this is taken into account an even greater advantagewould be realized by using the method of our invention.

The method of our invention may be applied to any fluid or mixture offluids such as hot solvents, hot gases, steam and hot water to name justa few. In each case the advantages are similar. Other mechanicalarrangements are those shown in FIGS. 1 and 3 may be envisioned andstill be within the scope of our invention. The types of reservoirs andhydrocarbons to which our invention is best suited are those in whichhot fluids are more efficient than cold fluids for the recovery of hydrocarbons. Prior-art is replete with information concerning hot fluidinjection and its advantages.

We claim:

1. A method for injecting a first fluid into a subterranean hydrocarbonreservoir via a cased well penetrating and in fluid communication withthe reservoir wherein there exists tubular means inside and open at somepoint to the annular space between the tubular means and the casing walland said first fluid is a mix ture of a second fluid injected down thetubular means and a liquid injected down the annulus comprisinginjecting said liquid into the annulus which liquid is initially at atemperature below the reservoir temperature,

injecting said second fluid into the tubular means at a temperatureabove the temperature of the reservoir before injection began in such away that the cooler liquid in the annulus is heated by the fluid in thetubular means to a temperature in excess of the reservoir temperature atabout the same time said liquid in the annulus reaches the depth of thehydrocarbon reservoir and injecting said first fluid into thehydrocarbon reservoir.

2. The method of claim 1 wherein said first fluid enters the reservoiras a liquid.

3. The method of claim 1 wherein said first fluid enters the reservoirpartially or completely vaporized.

4. A method for injecting a first fluid into a subterranean hydrocarbonreservoir via a cased well penetrating the reservoir wherein thereexists tubular means inside the well arranged to prevent fluidcommunication between the inside of the tubular means and the annularspace between the tubular means and the casing wall and wherein saidannular space is in fluid communication with the reservoir comprisinginjecting said first fluid as a liquid into the annular space betweenthe tubular means and the casing wall which liquid is initially belowreservoir temperature, I injecting a second fluid into the tubular meansat a temperature above the reservoir temperature before injection beganin such a way that said cooler first fluid in the annulus is heated bysaid second fluid in the tubular means to a temperature in excess of thereservoir temperature at about the same time said first fluid in theannulus reaches-the depth of the hydrocarbon reservoir and injectingsaid first fluid into the hydrocarbon reservoir. 5. The method of claim4 wherein said first fluid enters the reservoir as a liquid.

contacting said liquid in the well bore with a fluid en-- cased in saidtubular means wherein said fluid is at a temperature greater than thetemperature of the hydrocarbon reservoir and said liquid is initially ata temperature less than the temperature of the hydrocarbon reservoir andwherein the liquid exceeds the reservoir temperature at about the timethe liquid reaches the depth of the hydrocarbon reservoir.

1. A method for injecting a first fluid into a subterranean hydrocarbonreservoir via a cased well penetrating and in fluid communication withthe reservoir wherein there exists tubular means inside and open at somepoint to the annular space between the tubular means and the casing walland said first fluid is a mixture of a second fluid injected down thetubular means and a liquid injected down the annulus comprisinginjecting said liquid into the annulus which liquid is initially at atemperature below the reservoir temperature, injecting said second fluidinto the tubular means at a temperature above the temperature of thereservoir before injection began in such a way that the cooler liquid inthe annulus is heated by the fluid in the tubular means to a temperaturein excess of the reservoir temperature at about the same time saidliquid in the annulus reaches the depth of the hydrocarbon reservoir andinjecting said first fluid into the hydrocarbon reservoir.
 2. The methodof claim 1 wherein said first fluid enters the reservoir as a liquid. 3.The method of claim 1 wherein said first fluid enters the reservoirpartially or completely vaporized.
 4. A method for injecting a firstfluid into a subterranean hydrocarbon reservoir via a cased wellpenetrating the reservoir wherein there exists tubular means inside thewell arranged to prevent fluid communication between the inside of thetubular means and the annular space between the tubular means and thecasing wall and wherein said annular space is in fluid communicationwith the reservoir comprising injecting said first fluid as a liquidinto the annular space between the tubular means and the casing wallwhich liquid is initially below reservoir temperature, injecting asecond fluid into the tubular means at a temperature above the reservoirtemperature before injection began in such a way that said cooler firstfluid in the annulus is heated by said second fluid in the tubular meansto a temperature in excess of the reservoir temperature at about thesame time said first fluid in the annulus reaches the depth of thehydrocarbon reservoir and injecting said first fluid into thehydrocarbon reservoir.
 5. The method of claim 4 wherein said first fluidenters the reservoir as a liquid.
 6. The method of claim 5 wherein saidfirst fluid enters the reservoir partially or completely vaporized.
 7. Amethod for heating a liquid injected into the most external annularspace in an injection well bore containing tubular means wherein saidannular space is in communication with a subterranean hydrocarbonbearing reservoir which comprises contacting said liquid in the wellbore with a fluid encased in said tubular means wherein said fluid is ata temperature greater than the temperature of the hydrocarbon reservoirand said liquid is initially at a temperature less than the temperatureof the hydrocarbon reservoir and wherein the liquid exceeds thereservoir temperature at about the time the liquid reaches the depth ofthe hydrocarbon reservoir.